This volume consists of four chapters that cover a structurally diverse range of naturally occurring compounds. Chapter 1 delves into the chemistry of pyrogallols and their oxidized products, the hydroxy-o-quinones, including their role in cycloaddition reactions in the chemical synthesis of several fungal metabolites. Chapter 2 provides an in-depth description of the constituents of agarwood essential oil and smoke samples that are used in the perfumery industry, with an emphasis on the sesquiterpenoid and chromones constituents so far known. Chapter 3 discusses the defensive chemical ecology of two North American newt species that both produce tetrodotoxin, a well-known neurotoxin that causes paralysis and death in metazoans by disrupting electrical signals in the nerves and muscles. Chapter 4 discusses the limonoids and triterpenoids from the genus Walsura of the plant family Meliaceae, of which a number of species are utilized in several southeastern Asian countries in systems of folk medicine.